Add a flag to Dialect that allows for dialects to enable support for unregistered...

Add a flag to Dialect that allows for dialects to enable support for unregistered operations. This flag is off by default and can be toggled via the 'allowUnknownOperations(...)' method. This means that moving forward an error will be emitted for unknown operations if the dialect does not explicitly allow it.

    Example:

    func @unknown_std_op() {
      %0 = "std.foo_bar_op"() : () -> index
      return
    }

    Will result in:

    error: unregistered operation 'std.foo_bar_op' found in dialect ('std') that does not allow unknown operations

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PiperOrigin-RevId: 241266009